Vocal learning and control in songbirds, a system with many striking parallels to human speech, is used here as a model system to address general issues in the sensorimotor learning and control of complex behaviors. These issues include the production of sequences of stereotyped motor acts, the adaptive correction of errors in a motor plan, and the role of a basal ganglia circuit in adult motor control and plasticity. In the first part of this work, altered auditory feedback will be used to probe how this feedback is involved in both the on-line control of song production and in longer-term adaptive corrections to motor output. Specifically, mechanisms involved in the deterioration of song sequence under conditions of disrupted feedback will be investigated, as will the mechanisms involved in the active maintenance of adult song. In the second part, lesions in the "anterior forebrain pathway" (AFP), a basal ganglia-forebrain circuit strongly implicated in juvenile song learning, will be used to investigate the role of this circuit in adult song plasticity and production. These experiments will further our understanding of the avian song system and of the role of sensory feedback in motor learning and control, both generally and with particular relevance to human speech. [unreadable] [unreadable]